The present invention relates to a positive-working, light-sensitive mixture which contains, as the light-sensitive compound, a 1,2-naphthoquinone-2-diazidesulfonic acid ester of a condensation product formed from a bisphenol and formaldehyde. The light-sensitive mixture is intended particularly for the production of planographic printing plates.
Naphthoquinonediazidesulfonic acid esters of phenolic resins are known from German Pat. No. 865,860 (=U.S. Pat. No. 3,046,120). However, the copying materials obtained using these compounds are insufficiently sensitive to light and their resistance to developers and their elasticity are too low.
German Offenlegungsschrift No. 2,146,166 (=British Pat. No. 1,330,932) describes similar esters which have been prepared from condensation products of bisphenols with formaldehyde, in which the two phenolic nuclei of the bisphenol units are linked by oxygen or sulfur atoms or by sulfoxy, sulfonyl or optionally substituted methylene groups. The methylene groups can be substituted by lower alkyl groups, carboxyalkyl groups and phenyl groups. Methyl and ethyl groups are described as illustrative embodiments of lower alkyl groups. The compounds produce layers which have a good resistance to developers and good mechanical strength. They are used primarily for the production of etch resists. However, relatively strong alkaline solutions are required to develop them, and relief images made therewith have a tendency to become brittle, which manifests itself in a disadvantageous manner in the case of long printing runs in offset printing.
German Patent Application P 3,124,936.1 describes 1,2-naphthoquinone-2-diazidesulfonic acid esters of bis-hydroxyarylalkanes.